On Mon, Jul 29, 2019 at 7:50 PM Saeed Mahameed <sae...@mellanox.com> wrote:
>
> From: Vlad Buslov <vla...@mellanox.com>
>
> In order to remove dependency on rtnl lock, access to tc flows hashtable
> must be explicitly protected from concurrent flows removal.
>
> Extend tc flow structure with rcu to allow concurrent parallel access. Use
> rcu read lock to safely lookup flow in tc flows hash table, and take
> reference to it. Use rcu free for flow deletion to accommodate concurrent
> stats requests.
>
> Add new DELETED flow flag. Imlement new flow_flag_test_and_set() helper
> that is used to set a flag and return its previous value. Use it to
> atomically set the flag in mlx5e_delete_flower() to guarantee that flow can
> only be deleted once, even when same flow is deleted concurrently by
> multiple tasks.
>
> Signed-off-by: Vlad Buslov <vla...@mellanox.com>
> Reviewed-by: Jianbo Liu <jian...@mellanox.com>
> Reviewed-by: Roi Dayan <r...@mellanox.com>
> Signed-off-by: Saeed Mahameed <sae...@mellanox.com>
> ---
> @@ -3492,16 +3507,32 @@ int mlx5e_delete_flower(struct net_device *dev,
> struct mlx5e_priv *priv,
> {
> struct rhashtable *tc_ht = get_tc_ht(priv, flags);
> struct mlx5e_tc_flow *flow;
> + int err;
>
> + rcu_read_lock();
> flow = rhashtable_lookup_fast(tc_ht, &f->cookie, tc_ht_params);
> - if (!flow || !same_flow_direction(flow, flags))
> - return -EINVAL;
> + if (!flow || !same_flow_direction(flow, flags)) {
> + err = -EINVAL;
> + goto errout;
> + }
>
> + /* Only delete the flow if it doesn't have MLX5E_TC_FLOW_DELETED flag
> + * set.
> + */
> + if (flow_flag_test_and_set(flow, DELETED)) {
> + err = -EINVAL;
> + goto errout;
> + }
> rhashtable_remove_fast(tc_ht, &flow->node, tc_ht_params);
> + rcu_read_unlock();
>
> mlx5e_flow_put(priv, flow);
Dereferencing flow outside rcu readside critical section? Does a build
with lockdep not complain?
>
> return 0;
> +
> +errout:
> + rcu_read_unlock();
> + return err;
> }
>
> int mlx5e_stats_flower(struct net_device *dev, struct mlx5e_priv *priv,
> @@ -3517,8 +3548,10 @@ int mlx5e_stats_flower(struct net_device *dev, struct
> mlx5e_priv *priv,
> u64 bytes = 0;
> int err = 0;
>
> - flow = mlx5e_flow_get(rhashtable_lookup_fast(tc_ht, &f->cookie,
> - tc_ht_params));
> + rcu_read_lock();
> + flow = mlx5e_flow_get(rhashtable_lookup(tc_ht, &f->cookie,
> + tc_ht_params));
> + rcu_read_unlock();
> if (IS_ERR(flow))
> return PTR_ERR(flow);
Same, in code below this check?
